Integrated circuits incorporate complex electrical components formed in semiconductor material into a single device. Generally, an integrated circuit comprises a substrate upon which a variety of circuit components are formed wherein each of the circuit components are electrically isolated from each other. Integrated circuits are made of semiconductor material. Semiconductor material is material that has a resistance that lies between that of a conductor and an insulator. Semiconductor material is used to make electrical devices that exploit its resistive properties. A common type of structure is the metal-oxide semiconductor (MOS).
Semiconductor material is typically doped to be either a N type or a P type. N type semiconductor material is doped with a donor type impurity that generally conducts current via electrons. P type semiconductor material is doped with an acceptor-type impurity that conducts current mainly via hole migration. A N type or P type having a high impurity or high dopant concentration or density is denoted by a “+” sign. A N type or P type having a low impurity or low dopant concentration or density is denoted by a “−” sign.
Semiconductor devices are formed in a substrate of the integrated circuit. A typical semiconductor device is formed by selectively implanting dopants into the substrate to form device regions of either the P or N conductivity type. In addition, layers of dielectric material and metals are typically formed overlaying a surface of the substrate.
Some high reliability processes require a continuous silicon nitride (nitride) layer formed over the entire surface of the substrate of the integrated circuit. Generally, the nitride is deposited over the entire substrate surface by low pressure chemical vapor deposition (LPCVD) or plasma enhanced chemical vapor deposition (PECVD). The nitride layer is typically formed overlaying a patterned layer of silicon dioxide (oxide). The layer of nitride is used as a barrier to the diffusion of mobile ions. A diffusion barrier is desired because sodium and several other mobile ions tend to diffuse relatively rapidly to the surface of the substrate, which can degrade device performance. The layer of nitride is used to trap the mobile ions thereby prevention their diffusion to the surface of the substrate.
For improved performance, it is desired that the layer of nitride cover all of the oxide, even around the perimeter and sidewalls of contact openings through the oxide to the surface of the substrate. These contact openings are generally formed over device regions to provide a contact path. In forming nitride over oxide in sidewalls of contact openings, extra patterning steps that add cost to the manufacture of integrated circuits are required in the known art. It is desired in the art to form an integrated circuit with reduced process steps.
For the reasons stated above and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an integrated circuit with reduced process steps in forming an oxide sealed with nitride in contact openings.